For determining the composition of measured media, especially of liquids, such as, for example, pure liquids, liquid mixtures, emulsions or suspensions, various analytical measuring devices are applied in process measurements technology and in analytical measurements technology. An analytical measuring device includes, in general, a sensor, which is embodied to produce an electrical measurement signal dependent on at least one analytical measured variable of the measured medium, as well as an evaluating electronics, which ascertains from the measurement signal a measured value representing the current value of the at least one analytical measured variable in the measured medium. The analytical measured variable can be, for example, a concentration or activity of an analyte or a parameter dependent on a concentration or activity of at least one analyte in the measured medium. The terminology, analyte, means a substance contained, especially dissolved, in the measured medium and whose concentration in the measured medium is to be ascertained, and/or monitored, by means of the sensor. The evaluating electronics can be integrated at least partially in a measurement transmitter arranged directly at the measuring point in a housing with display and input means. At least a part of the evaluating electronics can also be arranged together with the sensor in a shared housing.
Such analytical measuring devices are applied in various fields, e.g., for monitoring and control of processes in pharmaceutical, chemical, biotechnological or biochemical production, however, also in processes for water treatment or waste water cleaning, as well as in environmental analytics. To the extent that an analytical measuring device is applied in a process, the measured medium is, as a rule, contained in a process container. Such a process container can be, e.g., a pipeline of a process installation or a reaction container, for example, a fermenter.
Sensors integrated into the wall of a process container for monitoring a measured variable of a measured medium contained in the process container are referred to as inline sensors. An inline sensor registers the measured variable directly in the measured medium to be monitored. Thus, inline sensors require no removal and pretreating of a sample from the process for determining the value of an analytical measured variable. Various adapters and assemblies, especially immersion or retractable assemblies, are known for integrating a sensor into a process wall. An arrangement, which includes an inline sensor integrated into the wall of a process container and, in given cases, an evaluating electronics connected with the inline sensor, but spaced therefrom, is referred to as an inline sensor arrangement. The inline sensor can be secured in the wall by means of a suitable adapter.
In the case of processes having to be performed under sterile, respectively aseptic, conditions, for example, processes in biotechnology, pharmacy or food technology, all parts of the process installation, especially all process containers and also sensors integrated therein, coming in contact with the process media, are, as a rule, sterilized, for example, thermally by heat, before beginning the process or between individual process steps. The heat sterilization can occur by dry heat (usually with hot air between 160° C. and 180° C. as sterilization medium) or by superheated steam as sterilization medium under increased pressure, for example, by autoclaving in a pressure vessel, i.e., so-called autoclaves. Typical, for example, are superheated steam sterilization processes, in which temperatures of at least 120° C. or more can occur. If the heat sterilization is performed in an autoclave, the process contacting parts of the process installation are (in given cases, already connected with one another) placed in the autoclave and sterilized there. The sterilized parts are then removed from the autoclave and placed in operation. Alternatively, a process installation can be sterilized by means of a so-called “sterilization in place” (SIP) method, in the case of which the process container and the inline sensor arrangements integrated therein are sterilized with superheated steam, which is introduced into the process container for a predetermined length of time. Inline sensor arrangements must, consequently, be able, without loss of functionality, to withstand the conditions, such as high temperatures and increased pressures arising in such case.
In bio-process measurement technology, for example, for monitoring and/or control of biotechnological processes, sensors are also applied, which have biological detection elements, e.g., elements, which in given cases as receptors, bind the analyte selectively and specifically. Biological detection elements can be proteins such as enzymes or antibodies, DNA/RNA fragments, cell organelles or entire cells and microorganisms. Such sensors are referred to as biosensors. After a typical superheated steam sterilization process, the receptors, such as biological detection elements of such biosensors, have, as a rule, greatly decreased activity. Most often, they are irreversibly denatured, i.e., no longer have their native 3-D structure (conformation). Such biosensors can, consequently, fundamentally not be simply inserted as inline sensors into the wall of a process container and then be sterilized along with the container by means of an established SIP process.
Many sensors with biological detection elements, e.g., those, which result from mesophilic organisms, which live in the temperature range of about 20-45° C., cannot be exposed to increased temperatures under SIP conditions, for example, above 80° C., without losing their functionality.
Described in the literature are sterilizable biosensors based on amperometric, enzyme sensors. M. Phelps, Development of a regenerable glucose biosensor sample for bioprocess monitoring, Master's Thesis, University of British Columbia, 1993, provides an overview of the literature of such sensors. Strategies described therein for assuring sterilizability of such biosensors while retaining their functionality comprise the bringing of the temperature sensitive receptors, arranged on a support, for example, comprising a working electrode, only after the sterilization process, into a reaction space within a sensor housing, which is closed off from the process container by a membrane permeable for the respective analyte. The membrane represents, in this case, the item that is sterilizable. In such case, the receptors can be present immobilized on the subsequently introduced working electrode or in a solution accommodated in the reaction space. During introduction of the receptors, the sterilizable item must not be damaged and this makes the handling of such inline sensor arrangements difficult.
Disadvantageous in the case of these inline sensor arrangements known from the literature is, besides the difficult handling, also that a fluctuating measuring performance of the biosensors can be observed. A reason for this is that the amount of the subsequently provided receptors is poorly reproducible. The previously known inline sensor arrangements, which comprise biosensors, are not practical, especially not as regards applications for monitoring industrial processes.
Known in the field of single-use technology frequently used for bio-processes are adapters or connectors, which enable the introduction of earlier sterilized sensors, e.g., earlier sterilized by means of gamma radiation, into a likewise earlier sterilized, single-use bioreactor (single-use fermenter). These connectors are, however, frequently not accepted, or not applicable, for use in a conventional process installation process container used multiple times for a plurality of process batches and regularly cleaned and sterilized according to one of the above described SIP sterilization methods.
The PALL Corporation of Port Washington, USA, offers, for example, connectors under the designation “Kleenpak II Sterile Connectors”, which serve for the introduction of liquids or probes, including sensors, into a single-use process container. These connectors are composed of two elements connectable with one another, wherein the two elements are sealed in their connection region in the non-connected state, in each case, with a withdrawable strip. The withdrawable strips are composed of aluminum foil with a polyester coating. For introducing a probe into the bioprocess, the first element of the connector can be connected with the process container and be sterilized with such, while the second element containing the probe can be sterilized with gamma radiation or autoclaving. For introducing the probe, the two connector elements are first connected loosely with one another, thereafter the withdrawable strips are removed by lateral withdrawal, then the two elements sealedly connected with one another and, finally, the probe is shifted by the first element of the connector into the process container.
An essential disadvantage of these connectors is that the connection between the two elements does not occur aseptically with sufficient assurance, since the two outer surfaces of the withdrawable strips of the elements are not sterile, or sterilizable, and, thus, in the case of withdrawal of these strips a risk of contamination remains. Furthermore, the risk of contamination is increased by the fact that directly after the withdrawal of the withdrawable strip the two elements are not sealedly connected with one another, whereby a contamination by the non-sterile environment cannot be excluded.
These connectors are also not designed for multiply usable, stainless steel, process containers sterilizable with SIP methods.